[PATCH] fs: gfs2: fix sleeping function called from invalid context

[Alessandro Zanni <alessandro.zanni87@gmail.com>]

The issue arises on a PREEMPT kernel because gfs2_quota_init
calls gfs2_qd_search_bucket while holding a bit spinlock and
triggering a "sleeping function called from invalid context"
bug.

This patch refactors the quota initialization by splitting the
lock into separate locks, moving the search outside the atomic
section and using RCU lock for a safe access without holding the
bit spinlock.

Modifications of this patch:
1. Use rcu_read_lock() around the invocation of the function
   gfs2_qd_search_bucket() for the search.
2. Add the spin_lock() around the insertion into the hash table
   and lists.
3. Remove the usage of unused spin_unlock().

Fixes: de0d95c26c41c ("gfs2: Check quota consistency on mount")
Reported-by: syzbot+642d0561f78362d67d3f@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=642d0561f78362d67d3f
Signed-off-by: Alessandro Zanni <alessandro.zanni87@gmail.com>
---
 fs/gfs2/quota.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
index 5290865f27f1..48516cbc8b49 100644
--- a/fs/gfs2/quota.c
+++ b/fs/gfs2/quota.c
@@ -1456,17 +1456,15 @@ int gfs2_quota_init(struct gfs2_sbd *sdp)
 			qd->qd_slot = slot;
 			qd->qd_slot_ref = 1;
 
-			spin_lock(&qd_lock);
-			spin_lock_bucket(hash);
+			rcu_read_lock();
 			old_qd = gfs2_qd_search_bucket(hash, sdp, qc_id);
+			rcu_read_unlock();
 			if (old_qd) {
 				fs_err(sdp, "Corruption found in quota_change%u"
 					    "file: duplicate identifier in "
 					    "slot %u\n",
 					    sdp->sd_jdesc->jd_jid, slot);
 
-				spin_unlock_bucket(hash);
-				spin_unlock(&qd_lock);
 				qd_put(old_qd);
 
 				gfs2_glock_put(qd->qd_gl);
@@ -1480,6 +1478,8 @@ int gfs2_quota_init(struct gfs2_sbd *sdp)
 
 				continue;
 			}
+			spin_lock(&qd_lock);
+			spin_lock_bucket(hash);
 			BUG_ON(test_and_set_bit(slot, sdp->sd_quota_bitmap));
 			list_add(&qd->qd_list, &sdp->sd_quota_list);
 			atomic_inc(&sdp->sd_quota_count);
-- 
2.47.3